Semiconductor devices, i.e., integrated circuits, are tested after packaging to identify those devices that are likely to fail shortly after being put into use. This test is described as a burn-in test. The burn-in test thermally and electrically stresses the semiconductor devices to accelerate the failure of those devices that would otherwise fail early on. This ensures that the devices sold to customers are more reliable.
The burn-in test can take many hours to perform and the temperature of the semiconductor devices is held in the range of about 100° C. to about 140° C. during those tests. During the burn-in test, the semiconductor devices are also subjected to ten percent (10%) to thirty percent (30%) higher than normal voltage. Consequently, since the power dissipation during burn-in is significantly higher than under normal operation, the extra power dissipation makes it even more difficult to control the temperature of the semiconductor device during burn-in. Although it is desirable to keep the temperature of the semiconductor device as high as possible during the burn-in in order to minimize the amount of time required for this test, the temperature must not be so high as to damage the semiconductor devices that are otherwise acceptable.
The latest semiconductor devices, especially microprocessors, have even higher electrical consumption in accordance with their higher frequency of operation. The higher electrical consumption causes the semiconductor devices to generate heat over 100 watts. In the burn-in of these devices, the heat generated when these devices are continuously connected with electricity at constant high temperature (e.g., about 125° C.) can be catastrophic. Unless these heat generating semiconductor devices are appropriately cooled to a controlled temperature, the burn-in testing equipment itself might be destroyed in addition to the semiconductor devices under test (DUTs).
One example of a prior art thermal control unit (TCU) for burn-in is illustrated in FIG. 3. Packaged semiconductor device 7 is attached to finned heat sink 9. Heater 8 is inserted between packaged semiconductor device 7 and heat sink 9. The heat generated by packaged semiconductor device 7 transfers to heat sink 9, where it is then dissipated. During the burn-in process, the temperature of the semiconductor device surface needs to be maintained within a desired temperature range (e.g., 100° C.±3°). The TCU has controller 11 to heat the device as required for maintaining the temperature of the packaged semiconductor device 7 within this range, while air is continuously circulated past fins 3.
In order to obtain the desired temperature range as illustrated in FIG. 3, temperature sensor 10 monitors the surface of the semiconductor device 7. If the measured temperature is lower than a certain specified temperature, controller 11 turns on heater 8 to heat the semiconductor device 7. As heater 8 warms up, the surface of semiconductor device 7 is directly heated to raise the temperature of the semiconductor device 7. On the other hand, when the temperature starts to exceed the upper limits of the prescribed range, heater 8 is turned off and the semiconductor surface is cooled by conducting heat away from the semiconductor device using heat sink 9. By repeatedly turning on and off the heater, the temperature of the semiconductor device surface can be maintained within the desired temperature range.
Another prior art configuration is illustrated in FIG. 4. This configuration also uses a finned heat exchanger 9 to cool the device, which is heated using heater 8. In this embodiment, the finned heat exchanger 9 is coupled to a source for circulating air to carry heat away from the heat sink 9. A fan 25 is provided to cool the finned heat exchanger 9. The greater the air flow, the greater the amount of cooling provided by the air flowing past the heat exchanger (at a given temperature). While not capable of fine temperature control, this configuration provides greater cooling capacity than a similar configuration with no air flow control capability.
Although the above-described temperature controllers utilize a finned heat sink cooled by air flowing past the fins, other prior art systems such as the one described in U.S. Pat. No. 7,199,597 use a liquid cooled heat exchanger. Another example of a TCU that uses liquid coolant for the heat exchanger used to cool a semiconductor device during burn-in is illustrated in FIG. 5. Semiconductor device 7 is attached to cooling cavity 420 with heater 480 being inserted between semiconductor device 7 and cooling cavity 420. Heat generated by the semiconductor device 7 is transmitted to cooling cavity 420 where it is absorbed by the cooling liquid running through cooling cavity 420. The cooling liquid enters from port 430 into the cooling cavity 420 and the temperature of the cooling liquid increases as it conducts heat away from semiconductor 7. The heated liquid exits cooling cavity 420 through port 440. This conducts heat away from the semiconductor device 7.
Accordingly, improved thermal controllers for monitoring the temperature of a device under test within a prescribed range are sought.